Browsing by Subject "Broadband absorbers"

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    ItemOpen Access
    Lithography-Free random bismuth nanostructures for full solar spectrum harvesting and mid-infrared sensing
    (WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2020) Soydan, Mahmut Can; Ghobadi, Amir; Yıldırım, Deniz Umut; Duman, E.; Bek, A.; Ertürk, Vakur Behçet; Özbay, Ekmel
    A lithography‐free, double‐functional single bismuth (Bi) metal nanostructure is designed, fabricated, and characterized for ultrabroadband absorption in the visible (vis) and near‐infrared (NIR) ranges, and for a narrowband response with ultrahigh refractive index sensitivity in the mid‐infrared (MIR) range. To achieve a large‐scale fabrication of the design in a lithography‐free route, the oblique‐angle deposition approach is used to obtain densely packed and randomly spaced/oriented Bi nanostructures. It is shown that this fabrication technique can provide a bottom‐up approach to controlling the length and spacing of the design. The characterization findings reveal a broadband absorbance above 0.8 in vis and NIR, and a narrowband absorbance centered around 6.54 µm. Dense architecture and extraordinary permittivity of Bi provide strong field confinement in ultrasmall gaps between nanostructures, and this can be utilized for a sensing application. An ultrahigh sensitivity of 2151 nm refractive‐index unit (RIU–1) is acquired, which is, as far as it is known, the experimentally highest sensitivity attained so far. The simple and large‐scale compatible fabrication route of the design together with the extraordinary optical response of Bi coating makes this design promising for many optoelectronic and sensing applications.
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    ItemOpen Access
    Metamaterials as broadband absorbers, tunable color filters, and multi-functional metasurfaces
    (2019-06) Aalizadeh, Majid
    Metamaterials have enabled us to come up with artificial structures and designs that can perform optical functionalities which are not achievable with natural materials. Here we design and implement three important applications of metamaterials as: 1. Ultra-broadband absorbers, 2. Real-time tunable color filters, and 3. Wideband and wide-angle efficient beam deflector and Multi-functional angular filter. By lithogra-phy being a major hinder on the way to mass production and cost-effectiveness, most of our works are lithography-free. We have introduced Manganese (Mn) for the first time as a very promising metal for broadband absorption and have used it in all our works. Four different Mn-based broadband absorbers are designed and fabricated in different chapters. Mn is used in the Metal-Insulator-Metal (MIM) cavity, annealed MIM configuration, top-layer-patterned MIM configuration, and random nanopyra-mids. It is shown in all works that Mn has a much better performance compared to other metals. For instance, in the work based on random nanopyramids, we obtain ultraviolet (UV) to far-infrared (FIR) perfect absorption by exploiting a lithography-free method and only by coating a single Mn layer on a high-roughness substrate. Moreover, using the combination of the MIM cavity and an electro-optic material, we have shown that a lithography-free color filter can be achieved that covers the whole visible spectrum by changing the voltage from -12 to 12 volts. Finally, in a structure composed of Silicon nano-rods, an ultra-wideband and wide-angle highly-efficient beam deflection is obtained. What makes the same structure very promising is that it also has multifunctional applications as band-pass, band-stop, and low-pass angular filter.